70 - Sciatic nerve

The sciatic nerve (also known as the ischiadic nerve and the ischiatic nerve) is a large nerve in humans.
It begins in the lower back and runs through the buttock and down the lower limb.
It is the longest and widest single nerve in the human body going from the top of the leg to the foot on the posterior aspect.
The sciatic supplies nearly the whole of the skin of the leg, the muscles of the back of the thigh, and those of the leg and foot.
It is derived from spinal nerves L4 through S3.
It contains fibres from both the anterior and posterior divisions of the lumbosacral plexus.

The nerve gives off articular and muscular branches:
The articular branches (rami articulares) arise from the upper part of the nerve and supply the hip-joint, perforating the posterior part of its capsule; they are sometimes derived from the sacral plexus.
The muscular branches (rami musculares) are distributed to the following muscles of the lower limb: biceps femoris, semitendinosus, semimembranosus, and the hamstring portion of adductor magnus.
The nerve to the short head of the biceps femoris comes from the common fibular part of the sciatic, while the other muscular branches arise from the tibial portion, as may be seen in those cases where there is a high division of the sciatic nerve.
The muscular branch eventually gives off the tibial nerve and common fibular nerve, which innervates the muscles of the (lower) leg.
The tibial nerve goes on to innervate all muscles of the foot except the extensor digitorum brevis (which is innervated by the common fibular nerve).
The sciatic nerve innervates the skin on the posterior aspect of the thigh and gluteal regions, as well as the entire lower leg (except for its medial aspect).

Pain caused by a compression or irritation of the sciatic nerve by a problem in the lower back is called sciatica.
Common causes of sciatica include the following lower back and hip conditions: spinal disc herniation, degenerative disc disease, lumbar spinal stenosis, spondylolisthesis, and piriformis syndrome.
Other acute causes of sciatica include coughing, muscular hypertension, and sneezing.
Sciatic nerve injury occurs between 0.5% and 2.0% of the time during total hip arthroplasty.
Sciatic nerve palsy is a complication of total hip arthroplasty with an incidence of 0.2% to 2.8% of the time, or with an incidence of 1.7% to 7.6% following revision.
Following the procedure, in rare cases, a screw, broken piece of trochanteric wire, fragment of methyl methacrylate bone cement, or Burch-Schneider metal cage can impinge on the nerve; this can cause sciatic nerve palsy which may resolve after the fragment is removed and the nerve freed.
The nerve can be surrounded in oxidized regenerated cellulose to prevent further scarring.
Sciatic nerve palsy can also result from severe spinal stenosis following the procedure, which can be addressed by spinal decompression surgery.

Bernese periacetabular osteotomy resulted in major nerve deficits in the sciatic or femoral nerves in 2.1% of 1760 patients, of whom approximately half experienced complete recovery within a mean of 5.5 months.
Sciatic nerve exploration can be done by endoscopy in a minimally invasive procedure to assess lesions of the nerve.
Endoscopic treatment for sciatic nerve entrapment has been investigated in deep gluteal syndrome; "Patients were treated with sciatic nerve decompression by resection of fibrovascular scar bands, piriformis tendon release, obturator internus, or quadratus femoris or by hamstring tendon scarring."

69 - Foramen Transversarium

The transverse foramen (Latin: foramen transversarium) pierces the transverse processes of the seven cervical vertebrae. In the upper six vertebrae, the foramen gives passage to the vertebral artery, vertebral vein, and a plexus of sympathetic nerves. The seventh foramen lacks the artery, but contains the vein and sympathetic nerves.

68 - Arc of Riolan

The superior mesenteric artery supplies the caecum, appendix, ascending colon and right two-thirds of the transverse colon via the ileocolic, right colic and middle colic branches. The ileocolic artery is formed as the distal continuation of the superior mesenteric artery in the root of the small bowel mesentery after the origin of the last ileal artery.

The inferior mesenteric artery is usually smaller in calibre than the superior mesenteric artery, and arises from the anterior or left anterolateral aspect of the aorta at about the level of the third lumbar vertebra, 3 or 4 cm above the aortic bifurcation and posterior to the horizontal part of the duodenum. It descends deep to the peritoneum, initially anterior and then to the left of the aorta. It crosses the origin of the left common iliac artery medial to the left ureter and then enters, and continues in, the root of the sigmoid mesocolon as the superior rectal artery. Distally the inferior mesenteric vein is lateral to it. The principal branches are the left colic, sigmoid (of which there may be several) and superior rectal artery.

The arc of Riolan (AOR) is also known as the meandering mesenteric artery or central anastomotic mesenteric artery. It is an inconstant artery that connects the proximal superior mesenteric artery (SMA) or one of its primary branches to the proximal inferior mesenteric artery (IMA) or one of its primary branches. It is classically described as connecting the middle colic branch of the SMA with the left colic branch of the IMA. It forms a short loop that runs close to the root of the mesentery.

When present, the AOR is an important connection between the SMA and IMA in the setting of arterial occlusion or significant stenosis. In proximal SMA occlusion, the AOR provides collateral flow from the IMA to the SMA territory. In proximal IMA occlusion, it provides collateral flow from the SMA to the IMA territory. In distal abdominal aortic occlusion it provides collateral flow from SMA to IMA to iliac vessels (via the superior rectal artery) and then to the lower limbs (via the external iliac artery).

67 - Anatomy of Knee

*I am not gonna explain the entire anatomy of the knee here, coz u will find that in hundreds of books. I am gonna post a video made by Dr. Bertram Zarins of the Mass General Hospital Sports Medicine Service, which has made me happy (happy because of its simplicity and beauty in explaining the basic anatomy). Sometimes you try explaining hundreds of things to students without a picture or video and they dont get it, but u show them a beautiful video or picture and they dont need you. This is one of those videos. Point to note is that the doctor was trying to explain Anterior cruciate ligament repair here and not anatomy.

Things to understand from this video :

1. The Anterior cruciate ligament ACL originates from deep within the notch of the distal femur. Its proximal fibers fan out along the medial wall of the lateral femoral condyle. There are two bundles of the ACL—the anteromedial and the posterolateral, named according to where the bundles insert into the tibial plateau. The ACL attaches in front of the intercondyloid eminence of the tibia, being blended with the anterior horn of the medial meniscus. These attachments allow it to resist anterior translation and medial rotation of the tibia, in relation to the femur.

2.The posterior cruciate ligament (or PCL) is one of the four major ligaments of the knee. It connects the posterior intercondylar area of the tibia to the medial condyle of the femur. This configuration allows the PCL to resist forces pushing the tibia posteriorly relative to the femur.

3. Medial collateral ligament : It is a broad, flat, membranous band, situated slightly posterior on the medial side of the knee joint. It is attached proximally to the medial condyle of femur immediately below the adductor tubercle; below to the medial condyle of the tibia and medial surface of its body. It resists forces that would push the knee medially, which would otherwise produce valgus deformity.

4. Lateral collateral ligament :  Rounded, more narrow and less broad than the medial collateral ligament, the fibular collateral ligament stretches obliquely downward and backward from the lateral epicondyle of the femur above, to the head of the fibula below. In contrast to the medial collateral ligament, it is fused with neither the capsular ligament nor the lateral meniscus. Because of this, the lateral collateral ligament is more flexible than its medial counterpart, and is therefore less susceptible to injury. The fibers of the posterior part of the ligament are short and incline backward as they descend; they are inserted into the tibia above the groove for the semimembranosus muscle.The anterior part of the ligament is a flattened band, about 10 centimeters long, which inclines forward as it descends.It is inserted into the medial surface of the body of the tibia about 2.5 centimeters below the level of the condyle. It resists forces that would push the knee laterally, which would otherwise produce a varus deformity.

*Other important structures related to knee anatomy are the menisci of the knee and the bursa surrounding the knee, which i am gonna discuss in another post someday.

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Now try answering these Multiple choice questions (mcqs):

1.Posterior Cruciate ligament prevents
a.Anterior movement of tibia in relation to femur
b.Posterior movement of tibia in relation to femur
c.Medial movement of tibia
d.Lateral movement of tibia

answer b.posterior ...

2.Anterior cruciate ligament prevents
a.Anterior movement of tibia in relation to femur
b.Posterior movement of tibia in relation to femur
c.Medial movement of tibia
d.Lateral movement of tibia

answer a.anterior....

3.Medial collateral ligament prevents
a.Anterior movement of tibia in relation to femur
b.Posterior movement of tibia in relation to femur
c.Medial movement of tibia
d.Lateral movement of tibia

answer c. medial...

4.Lateral collateral ligament prevents
a.Anterior movement of tibia in relation to femur
b.Posterior movement of tibia in relation to femur
c.Medial movement of tibia
d.Lateral movement of tibia

answer d.lateral...

5.What are the two bundles ACL is made up of
a.Anteromedial and posterolateral
b.Posteromedial and anterolateral
c.Mediolateral and cephalocaudal
d.None of the above

answer a. AM and PL.

66 - Torcular herophili

The confluence of sinuses or torcular herophili is the connecting point of the superior sagittal sinus, straight sinus, and occipital sinus. It is found deep to the occipital protuberance of the skull. Blood arriving at this point then proceeds to drain into the left and right transverse sinuses.

The superior sagittal sinus often drains into (either exclusively or predominantly) one transverse sinus, and the occipital sinus drains into the other. Confluence of sinuses An older term often used for the confluence of sinuses "torcular herophili", describes the veins as a gutter, or canal, and honors Herophilos, the Greek anatomist who was the first to use cadavers for the systematic study of anatomy. This term more precisely refers to the concavity in the bone which is the location of the confluence of sinuses.

65 - Truesdale's Triangle

Anatomic area formed at lower end of thoracic esophagus by diaphragm inferiorly, pericardium anteriorly and superiorly, and descending aorta posteriorly.

For those wondering about the importance of this triangle, this traingle contains the esophagus and helps the surgeons performing various oesophageal surgical procedures like thoracoscopic oesophagomyotomy. The surgeons approach the esophagus in the inferior mediastinum through this triangle.

64 - Transpyloric plane

An upper transverse line also known as Addison's Plane, located halfway between the jugular notch and the upper border of the pubic symphysis. It is also said to lie roughly a hand's breadth beneath the xiphoid process of the human sternum. The plane in most cases cuts through the pylorus of the stomach, the tips of the ninth costal cartilages and the lower border of the first lumbar vertebra.

 The transpyloric plane is clinically notable because it passes through several important abdominal structures. These include:

1. lumbar vertebra 1 and hence passes just before the end of the spinal cord in adults. 
2. the fundus of the gallbladder 
3. the neck of the pancreas 
4. the pancreatic body 
5. the origin of the superior mesenteric artery from the abdominal aorta and 
6. termination of the superior mesenteric vein at the hepatic portal vein 
7. the left and right colic flexure  
8. hilum of the kidney on the left  
9. upper pole of the kidney on the right 
10. the root of the transverse mesocolon 
11. duodenojejunal flexure 
12. the 1st part of the duodenum 
13. the upper part of conus medullaris 
14. the spleen 
15. the pylorus of the stomach which will lie at this level approximately 5 cm to the right of the midline.

p.s: I want the readers to note that the image depicted above shows the transpyloric plane to be passing through the hilum of both kidneys, which infact is not true. The transpyloric plane actually passes through the upper pole of right kidney and the hilum of left kidney as mentioned in the description below the image. The cause of the error is probably because the artist depicted both the kidneys at equal height rather than the actual fact that the right kidney is inferior to the left kidney due to the liver above.

63 - Scalene Muscles

The scalene muscles are a group of three pairs of muscles in the lateral neck, namely the scalenus anterior, scalenus medius, and scalenus posterior. They are innervated by the spinal nerves C4-C6.

 The Scalenus anterior (Scalenus anticus), also known as anterior scalene muscle, lies deeply at the side of the neck, behind the Sternocleidomastoideus. It arises from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebræ, and descending, almost vertically, is inserted by a narrow, flat tendon into the scalene tubercle on the inner border of the first rib, and into the ridge on the upper surface of the rib in front of the subclavian groove. It can be involved in certain forms of Thoracic outlet syndrome.

 The Scalenus medius, the largest and longest of the three scalene muscles, arises from the posterior tubercles of the transverse processes of the lower six cervical vertebræ. It descendes along the side of the vertebral column to insert by a broad attachment into the upper surface of the first rib, between the tubercle and the subclavian groove. The brachial plexus and the subclavian artery pass anterior to it. Because it elevates the upper ribs, the middle scalene muscle is also one of the accessory muscles of respiration. The

Scalenus posterior (Scalenus posticus), the smallest and most deeply seated of the three Scaleni, arises, by two or three separate tendons, from the posterior tubercles of the transverse processes of the lower two or three cervical vertebræ, and is inserted by a thin tendon into the outer surface of the second rib, behind the attachment of the Scalenus anterior. It is occasionally blended with the Scalenus medius.